GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 3.1 69 Xu S., Y. Zhang, and G. Lambare, 2005a, Antileakage fourier transform for seismic data regularization in higher dimensions: Geophysics, 70, WB113–WB119. Xu S., Y. Zhang, D. Pham, and G. Lambare, 2005b, Antileakage Fourier transform for seismic data regularization: Geophysics, 70, V87–V95. Zwartjes P. M., and M. D. Sacchi, 2004, Fourier reconstruction of non-uniformly sampled, aliased data: 74th Annual International Meeting, SEG, Expanded Abstracts, 1997–2000. non linear imaging with internal multiples C. Fortini, V. Lipari Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Italy Introduction. Conventional seismic imaging algorithms are based on single-scattering hypothesis ( linear imaging ). The reverberations that generate during wavefield propagation in the subsurface ( multiple reflections ) are usually considered as unwanted noise. Even though the most energetic reverberations (especially in marine seismic acquisition) are the so called surface-related multiples, in areas of high structural complexity we usually record also strong internal and intra-salt multiples . The most common approach used to handle with the presence of multiple reflections (both surface and internal) in the acquired seismic data is to try to eliminate them. First, a model of the multiples is built by means of either model-based or data-driven methods and then the noise model is adaptively subtracted from the original data (Verschuur, 2006; Verschuur et al. , 1992; Lipari et al. , 2012). However, the multiply scattered recorded events had interacted with the subsurface discontinuities and thus carry useful information about it. When properly imaged, these events can enhance the seismic image and may provide additional illumination in those areas poorly imaged by conventional approaches. Recently, researches onmultiples have shifted their focus on the exploitation onwhat has been often considered only as noise: both surface-related and internal multiples have been proved to carry useful information about the subsurface discontinuities. Berkhout and Verschuur (2006) showed that the multiple reflections can be used to re-create the associated primaries and then exploited for imaging purposes. They also proved that multiples carry useful information and can thus enhance the overall understanding of the subsurface structure. Various authors showed that WE (Wavefield Extrapolation) migration algorithms can be effectively used for the imaging of the multiple reflections (examples can be found in Guitton (2002), Muijs (2007), Alkhalifah (2011)). However, in scenarios characterized by the presence strong reflective interfaces (carbonates layers, salt-bodies,…) we expect to record also relatively strong internal multiples. Recently various authors have proposed new non-linear imaging methods (Ravasi and Curtis, 2013; Vasconcelos and Hornby, 2008; Fleury, 2013; Malcolm et al., 2009; showing that these techniques help in reducing the image artifacts and improve the resolution and illumination of the subsurface image provided by conventional techniques. The main advantage of these new techniques resides in the use of the internal multiples events. Here, we propose a technique based on non-linear wave eld datuming and seismic interferometry that allows us to separately exploit the information coming from the internal multiples recorded in a conventional seismic acquisition. Wavefield datuming is a means of extrapolating a recorded seismic data from one surface to another. From a numerical point of view, it can relocate the source and receiver locations while keeping the propagation features. The seismic data recorded at the original (actual) acquisition surface are used to generate a new seismic dataset with a new (virtual) acquisition geometry deployed at an arbitrary position in the subsurface (Liu and Xu, 2011; Berryhill, 1979, 1984). For the specific applications presented in this paper, the original wave eld is used as input to reconstruct a new virtual seismic